In a traveling wave amplifier or oscillator, a stream of electrons interact on a propagating electromagnetic wave, causing the electromagnetic wave to be amplified. In order to achieve the desired interaction, the electromagnetic wave is propagated along a slow-wave structure, such as helical slow-wave structure. The slow-wave structure provides a path of propagation for the electromagnetic wave, and the path is longer than the axial length of the structure so that the electromagnetic wave can propagate axially at the velocity of the electron stream.
The helical slow-wave structure is a critical component in the traveling wave amplifiers or oscillators, and its helix is supported within an encasing barrel by means of a plurality of electrically insulating rods, which are positioned equally, circumferentially around the helix. In a high power traveling wave amplifier or oscillator, electron beam interaction and RF losses can produce a lot of heat, leading to high operating temperature.
For traveling wave amplifiers or oscillators working at small and medium power, the slow-wave structure is assembled by cold stuffing/fitting technology or hot insertion method. A conventional helical slow-wave structure is shown in FIG. 1 and FIG. 2. The helix 3 is made of tungsten or molybdenum, the supporting rods 2 are made of beryllia or boron nitride, and the encasing barrel 1 is made of stainless steel. Using conventional assembly, the contact area between helix 3 and supporting rods 2 is a line before assembling and only a narrow side after assembling, far smaller than the width d of supporting rods 2 as shown in FIG. 2. The thermal contact resistance between helix 3 and supporting rods 2 is very large, thus the helical slow-wave structure in prior art has bad heat dissipation capability.
In order to enhance heat dissipation capability and thereby increase output power of the helical traveling wave amplifiers or oscillators, the helix 3 is brazed to the dielectric supporting rods 2 that are brazed to encasing barrel 1. This method can increase the contact area and decrease thermal contact resistance between various components of the helical slow-wave structure, but the process of assembly is very complex, and the accumulation of the solder can cause strong reflection of the electromagnetic wave, even induce oscillation in the traveling wave amplifiers or oscillators.
In order to overcome the deficiencies cited above, diamond is used as the material of the supporting rods 2 in the slow-wave structure, which is reported in U.S. Pat. No. 6,917,162 B2. Although diamond has high thermal conductivity, the process of assembly is also very complex and the cost of diamond is very expensive, so it is not widely used.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.